What historically happens to those groups that break away from Rome is that they lose their moral compass. The Eastern Orthodox Churches allow divorce and re-marriage.

I don't want to derail this thread, but I constantly see this idea that the East started allowing for divorce and re-marriage after the East-West schism thrown around as if it were a fact, but it is simply untrue. If one will examine chapter nine of St. Basil's epistle 188, to Amphilochius, concerning the canons (also known as his First Canonical Epistle) Basil writes about when it is possible for a man to leave his wife and live with another woman without the new relationship being adulterous. The allowance for divorce and remarriage in the East then, can be no younger than 1633 years old (St. Basil reposed in the year 379), and considering that Basil references what is allowed by custom as opposed to what should be allowable in theory, the practice must be even older still.

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But God, he says, is simple, and whatever attribute of Him you have reckoned as knowable is of His essence. But the absurdities involved in this sophism are innumerable. When all these high attributes have been enumerated, are they all names of one essence? St. Basil Letter 234

My comments on the above: The pope may be the highest interpreter of Canon Law, but he is not the arbiter of abjective facts. It is no disrespect to the Pope or the Papacy to admit that. If I personally find myself in a State of Emergency, and the Pope tells me I am not, the pope might be wrong. He might not have the full facts at his disposal.

The lifting of the Decree of Excommunication is, on the argument of the SSPX and those taking this opinion (and there are many of the highest standing, not formally affiliated to the SSPX) who maintain that the lifting of the decree was 'without prejudice' to whether it was invalid in the first place. I can see that, in a general way, this could be the case. The imposition of Excommunication is a disciplinary measure over and above the original offence. It could be lifted for a number of reasons, including 'a quiet gestiure of reconciliation '(which led to a huge uproa' - Pope Benedict's phrase)' as Pope Benedict put it in the case of the SSPX. But in the general case, the pope, according to Vatican I, is infallible only when pronouncing definitively on a question of Faith and/or Morals. He can be mistaken on questions of fact. ..Ttherefore there is a theoretical possibility that a decree of excommunication can be issued incorrectly. The historical record, accepted by the Fathers of Vatican I, is that S. Athanasius was excommuunicated with the endorsment of Pope Liberius. Athanasius did not argue, he simply continued with his work. If such a decree were subsequently lifted, it would not prove ipso facto that the original excommunication was valid.